Q: I have a hull hydrostatic model and a hull structural model, whereby I compare the deflections of the two models. The structural model is composed of two longitudinal beams and some transverse link beams, both made up of prismatic sections. The deflection results do not compare nicely. Why is it so?
REV 5.10

A: Without having the data it is impossible to say exactly what is going on, but:

• Never model the structure of a vessel as two beam (unless,of course, you are modeling a catamaran). It is impossible to get the shear and torsion correctly this way. Use either a single beam or a complete beam/plate model.
• Is the difference a rigid motion? Longitudinal strength uses a beam pinned at the bow and stern, did you restrain your structural model the same way?
• The answers will never be exactly the same because of the way the load is applied for a structural analysis.